Light delivery waveguide

ABSTRACT

A light source and a waveguide are mounted on a recording head slider. Light rays are emitted from the light source into the waveguide. The waveguide may include two core layers for light ray transmission. The first core layer enhances light coupling efficiency from the light source to the second core layer. The second core layer transforms a profile of the light. The waveguide may include a tapered portion with a narrow opening near the light source and a wider opening near the tapered portion exit. The light rays passing through the waveguide may be directed toward a collimating mirror. The collimating mirror makes the light rays parallel or nearly parallel and re-directs the light rays to a focusing mirror. The focusing mirror focuses the collimated light rays to a spot on a magnetic media disc.

BACKGROUND

“Heat assisted magnetic recording,” optical assisted recording orthermal assisted recording (collectively hereinafter HAMR), generallyrefers to the concept of locally heating a recording medium to reducethe coercivity of the recording medium so that an applied magneticwriting field can more easily affect magnetization of the recordingmedium during a temporary magnetic softening of the recording mediumcaused by the local heating. HAMR allows for the use of small grainmedia, which is desirable for recording at increased areal densities,with a larger magnetic anisotropy at room temperature assuring asufficient thermal stability. HAMR can be applied to any type of storagemedia, including for example, tilted media, longitudinal media,perpendicular media, and/or patterned media.

When applying a heat or light source to the magnetic medium, it isdesirable to confine the heat or light to a track where writing istaking place and to generate the write field in close proximity to wherethe magnetic medium is heated to accomplish high areal densityrecording. In addition, one of the technological hurdles to overcome isto provide an efficient technique for delivering large amounts of lightpower to the recording medium confined to sufficiently small opticalspots.

One way to achieve tiny confined hot spots is to use a near-fieldtransducer, such as a plasmonic optical antenna or an aperture,integrated in a waveguide. Light propagating in the waveguide is focusedby a focusing element, such as a planar solid immersion mirror into thenear-field transducer. However, one of the challenges is to direct thelight into the waveguide in a slider associated with the magneticrecording head with low cost, good alignment tolerance, and high lightdelivery efficiency. Systems and methods for achieving laser-in-sliderlight delivery are disclosed herein.

SUMMARY

In one implementation, a waveguide has a first core layer configured toreceive light from a light source and transmit the light at a first modeprofile associated with the light source. The waveguide also has atapered portion of a second core layer configured to receive the lightfrom the first core layer and transform the light to a second moreconfined mode profile.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the Detailed.Description. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. These andvarious other features and advantages will be apparent from a reading ofthe following detailed description.

BRIEF DESCRIPTIONS OF THE DRAWINGS

The described technology is best understood from the following Detailed

Description describing various implementations read in connection withthe accompanying drawings.

FIG. 1 illustrates a plan view of an example disc drive.

FIG. 2 illustrates an example partial isometric view of a trailingsurface of a transducer head slider configured to fly in close proximityto a magnetic media disc with cladding layers, core layers, a laserdiode, a waveguide, and mirrors mounted thereon.

FIG. 3 is an example cross-section of a laser-in-slider light deliverysystem including a laser diode, cladding layers, and core layers, with afirst mode profile and a second mode profile superimposed on therespective core layers.

FIG. 4A is an example cross-section of a laser-in-slider light deliverysystem with one first core layer and two second core layers.

FIG. 4B is an example cross-section of a laser-in-slider light deliverysystem with a third cladding layer located between a first core layerand a second core layer.

FIG. 4C is an example cross-section of a laser-in-slider light deliverysystem with a second core layer below a first core layer.

FIGS. 5A-5F illustrate an example series of mode profiles representinglight passing through a waveguide at various distances from a laserdiode.

FIGS. 6A-6B illustrate example positioning tolerances of a laser diodewith respect to the waveguide of FIGS. 5A-5F.

FIG. 7A illustrates light passing through a waveguide and reflecting offof an example collimating mirror.

FIG. 7B illustrates collimated light reflecting off of an examplefocusing mirror and converging at a focusing point.

FIG. 8A illustrates an example laser-in-slider light delivery system,where a collimating mirror is oriented so that light rays reflectingfrom the collimating mirror propagate toward an angled, double-sided,focusing mirror.

FIG. 8B illustrates an example laser-in-slider light delivery systemwhere a collimating mirror is oriented so that light rays reflectingfrom the collimating mirror propagate toward an angled, single-sided,focusing mirror.

FIG. 9B illustrates an example laser-in-slider light delivery systemwhere a straight minor and a split straight mirror are used to shiftlight rays reflecting from the collimating mirror.

FIG. 10 is a flow chart illustrating example operations for directinglight from a light source, through a waveguide, and focusing the lighton a magnetic media for heat assisted magnetic recording.

DETAILED DESCRIPTIONS

FIG. 1 illustrates a plan view of an example disc drive 100. The discdrive 100 includes a base 102 to which various components of the discdrive 100 are mounted. A top cover 104, shown partially cut away,cooperates with the base 102 to form an internal, clean environment forthe disc drive in a conventional manner. The components include aspindle motor 106 that rotates one or more storage medium discs 108 at aconstant high speed. Information is written to and read from tracks onthe discs 108 through the use of an actuator assembly 110, which rotatesduring a seek operation about a bearing shaft assembly 112 positionedadjacent the discs 108. The actuator assembly 110 includes a pluralityof actuator arms 114 that extend towards the discs 108, with one or moreflexures 116 extending from each of the actuator arms 114. Mounted atthe distal end of each of the flexures 116 is a head 118 that includesan air bearing slider enabling the head 118 to fly in close proximityabove the corresponding surface of the associated disc 108. The distancebetween the head 118 and the storage media surface during flight isreferred to as the fly height.

During a seek operation, the actuator assembly 110 pivots about thebearing shaft assembly 112 and the transducer heads 118 are caused tomove across the surfaces of the discs 108. A flex assembly 130 providesthe requisite electrical connection paths for the actuator assembly 110while allowing pivotal movement of the actuator assembly 110 duringoperation. The flex assembly 130 also provides power for an on-sliderlaser light source.

In one implementation, the laser light source 119 (e.g., a laser diode)or other light source (e.g. a light emitting diode (LED)) is mounted ona trailing surface of the head 118 slider. Light from the laser lightsource 119 is directed into one or more core layers and through awaveguide also on the trailing surface of the head 118 slider. The lightis then redirected and/or focused on a point on the disc 108 in closeproximity to a write pole on the head 118 with mirrors. A near-fieldtransducer (NFT) may also be mounted on the head 118 slider to furtherconcentrate the light on the point on the disc 108. In anotherimplementation, one or more of the laser light source 119, core layers,waveguide, mirrors, and/or NFT is mounted on an area of the head 118away from the slider or on a head 118 slider surface other than thetrailing surface.

FIG. 2 illustrates an example partial isometric view of a trailingsurface of a transducer head slider 202 configured to fly in closeproximity to a magnetic media disc 204 with cladding layers 206, 208,core layers 210, 212, a laser diode 214, a waveguide 216, and mirrors218, 220 mounted thereon. The cladding layers 206, 208, core layers 210,212, laser diode 214, waveguide 216, and mirrors 218, 220 collectivelyform one implementation of a laser-in-slider light delivery system 200.

The slider 202 is located at one end of an actuator arm and is suspendedabove the magnetic media disc 204 with a suspension 222, sometimesreferred to as flexures. The suspension 222 enables the slider 202 tofly in closed proximity above the disc 204 as the disc 204 rotatesduring operation. The laser-in-slider light delivery system 200 is shownattached to a trailing surface of the slider 202, although the system200 may be attached to other surfaces of the slider 202 and/ortransducer head in other implementations.

A laser light source (e.g., the laser diode 214) or other light source(e.g., a light emitting diode (LED)) is shown mounted on the trailingsurface of the slider 202. Immediately adjacent to the laser diode 214is a first cladding layer 206 that separates the core layers 210, 212from the slider 202. The core layer 210 is deposited substantially ontop (in the X-direction) of the first cladding layer 206. The secondcore layer 212 is likewise deposited on top (in the X-direction) of thefirst core layer 210.

In an example manufacturing process, the first cladding layer 206 isfirst deposited on the slider 202. The first core layer 210 is depositedon top of the first cladding layer 206. The second core layer 212 isthen deposited on top of the first core layer 210. A tapered portion 217of the waveguide 216 adjacent to the laser diode 214 is then formed onthe waveguide 216 by etching areas of the second core layer 212 adjacentthe tapered portion 217 down to the first core layer 210. In someimplementations, the etching is accomplished by photolithography. Asecond cladding layer 208 is then deposited on top of the second corelayer 212.

Light rays 234 (illustrated by small arrows in FIG. 2) are emitted fromthe laser diode 214 (which in some implementations is an edge-emittinglaser diode 214) and coupled into the waveguide 216 generally in theZ-direction. The waveguide 216 includes the first core layer 210 and thesecond core layer 212 for light ray 234 transmission and the firstcladding layer 206 and the second cladding layer 208 to confine thelight rays 234 to the first core layer 210 and the second core layer212. As such, the cladding layers 206, 208 include materials that aredielectric and have a low index of refraction (e.g., Al₂O₃, SiO₂, andMgF₂).

While core layers 210, 212 are also dielectric, they have higher indicesof refraction than the cladding layers 206, 208. The first core layer210 functions to enhance light coupling efficiency from the laser diode214 to the second core layer 212. The tapered portion 217 of thewaveguide 216 on the second core layer 212 functions to couple the lightpropagating in the first core layer 210 into the second core layer 212where the light is confined to a tighter mode profile. The mode profileof the light refers to a dimensional size and shape of an XY-plane crosssection of the light as a function of light intensity (see FIGS. 5A-5F).As such, the first core layer 210 includes materials that have an indexof refraction lower than the second core layer 212, but slightly higherthan the cladding layers 206, 208 (e.g., SiON, ZnS, and SiO₂). Thesecond core layer uses dielectric material with a high index ofrefraction (e.g., Ta₂O₅, TiO_(x), SiN_(x), SiC, and ZnS).

In the implementation shown in FIG. 2, the first core layer 210 and thesecond core layer 212 are intact in a region occupied by the mirrors218, 220. A portion of the second core layer 212 is etched away withinthe waveguide 216 to form the tapered portion 217 in the second corelayer 212. In other implementations, the first core layer 210 or boththe first core layer 210 and second core layer 212 is etched away withinthe waveguide 216 to form the tapered portion 217. The tapered portion217 of the waveguide 216 of FIG. 2 has a linear taper in the Z-directionwith a narrow opening near the laser diode 214 where the light entersthe waveguide 216 (i.e., the waveguide entrance) and a wider openingwhere the light exits the tapered portion 217 of the waveguide 216.However, in other implementations, the tapered portion 217 may benon-linear and encompass a variety of shapes optimized to achieve a fastmode transformation from the first core layer 210 to the second corelayer 212.

A width of the tapered portion 217 of the waveguide 216 at the taperedportion 217 exit is selected such that the light rays 234 exiting thetapered portion 217 have a minimum amount of divergence but are stillsingle-mode with a Gaussian-like spatial profile in the XY plane. Insome implementations the light rays 234 exiting the tapered portion 217are at a fundamental mode. The width of the tapered portion 217 exit maybe chosen as wide as possible so that the light rays 234 can becollimated with a collimating mirror 218 having a low numerical aperturein-plane to achieve a manufacture tolerance. In implementations thatutilize a channel waveguide to guide the light rays 234 from the taperedportion 217 to an air-bearing surface or near the air-bearing surfacewhere a near-field transducer may be placed, the width of the taperedportion 217 exit and the waveguide taper is optimized so that the lightrays 234 propagating in the channel waveguide are tightly confined.

Light rays 234 exiting the tapered portion 217 are directed toward thecollimating mirror 218, an off-axis, single sidewall, parabolic mirror.The collimating mirror 218 makes the divergent light rays 234 exitingfrom the tapered portion 217 of the waveguide 216 parallel or nearlyparallel and re-directs the collimated light rays 234 to the focusingmirror 220. The collimated light rays 234 proceed to the focusing mirror220 in the negative Y-direction with little divergence in theZ-direction or X-direction. The focusing mirror 220, a double sidewall,parabolic mirror, focuses the collimated light rays 234 to adiffraction-limited optical spot 224. In some implementations, thediffraction-limited optical spot 224 is focused on a location on themagnetic media disc 204. In other implementations, thediffraction-limited optical spot 224 focuses on a near-field transducer.The near-field transducer serves to further condense the light rays 234to a location on the magnetic media disc 204.

FIG. 2 illustrates one orientation of the collimating mirror 218 and thefocusing mirror 220. However, other implementations may vary the size,shape, and/or orientation of the collimating mirror 218 and the focusingmirror 220 (see e.g., FIGS. 8A-9B). Further, some implementations mayalso utilize straight mirrors to redirect the light rays 234 and/orintroduce a phase shift in the mode profile of the light.

The second cladding layer 208 (shown detached in FIG. 2) is depositedadjacent the laser diode 214 and substantially on top (in theX-direction) of the second core layer 214. The second cladding layer 208may be thicker in the area of the waveguide 216 to fill in space aroundthe tapered portion 217 created by etching away the second core layer212. A write pole 226 may be incorporated into the second cladding layer208 or mounted in close proximity to the second cladding layer 208. Whenfully assembled, the system 200 creates the diffraction-limited opticalspot on the magnetic media disc in close proximity to the write pole226. Thus, heat assisted magnetic recording on the magnetic media disc204 is accomplished.

FIG. 3 is an example cross-section of a laser-in-slider light deliverysystem 300 including a laser diode 314, cladding layers 306, 308, andcore layers 310, 312 with a first mode profile 328 and a second modeprofile 330 superimposed on the respective core layers 310, 312. Thelaser diode 314 and the first cladding layer 306 are mounted on asurface of a transducer head slider 302. In other implementations, thelaser diode 314 is mounted to the second cladding layer 308. The firstcore layer 310, the second core layer 212, and the second cladding layer308 are deposited on top (in the X-direction) of the first claddinglayer 306. A combination of the cladding layers 306, 308 and the corelayers 310, 312 make up a waveguide 316. One example cross-section ofthe laser-in-slider light delivery system 300 is illustrated by atop-down view of FIG. 2.

A thickness of the first core layer 310 in the X-direction is selectedso that a first mode profile 328 of light within the first core layer310 of the waveguide 316 best matches a mode profile of the laser diode314 light output. A thickness of the second core layer 312 in theX-direction is selected to yield a tightly confined mode profile. Lightrays (represented by arrows) emitting from the laser diode 314 firstenter the first core layer 310 and then transfer to the second corelayer 312 through adiabatic mode transformation along a length of atapered portion of the waveguide 316 in the Z-direction. The taperedportion fabricated on the second core layer 312 is optimized so that thelight is efficiently transformed from the first core layer 310 to thesecond core layer 312.

In the implementation of FIG. 3, the laser diode 314 is shown mountedwithin a cavity formed in the transducer head slider 302. However, inother implementations (see e.g. FIGS. 4A-4C), the laser diode 314 isshown mounted directly on a planar surface of the transducer head slider302 without using a cavity. Further, FIG. 2 shows the laser diodethickness in the X-direction as greater than the thickness of thecladding layers 306, 308, and core layers 310 combined in theX-direction. However, in other implementations, the aforementionedthicknesses may be the same or the laser diode thickness may be lessthan the thickness of the cladding layers 306, 308, and core layers 310combined.

FIG. 4A is an example cross-section of a laser-in-slider light deliverysystem 400 with two first core sub-layers 410 and one second core layer412. Here, light rays (represented by arrows) emitting from a laserdiode 414 enter a waveguide 416 through the two sub-layers 410 of thefirst core layer that sandwich the second core layer 412. The secondcore layer 412 includes a waveguide 416 with a tapered portion. As thelight rays pass through the waveguide 416, the light rays are graduallytransferred through the tapered portion formed on the second core layer412 from each of the first core sub-layers 410. The light rays exit thetapered portion of the waveguide 416.

FIG. 4B is an example cross-section of a laser-in-slider light deliverysystem 405 with a third cladding layer 432 located between a first corelayer 410 and a second core layer 412. Here, light rays (represented byarrows) emitting from a laser diode 414 enter a waveguide 417 through afirst core layer 410. The second core layer 412 includes a waveguide 417with a tapered portion. As the light rays pass through the waveguide417, the light rays are gradually transferred by resonant tunnelingthrough the third cladding layer 432 to the tapered portion formed onthe second core layer 412 from the first core layer 410. The light raysexit the tapered portion of the waveguide 417.

FIG. 4C is an example cross-section of a laser-in-slider light deliverysystem 415 with a second core layer 412 below a first core layer 410.Here, light rays (represented by arrows) emitting from a laser diode 414enter a waveguide 419 through a first core layer 410. The second corelayer 412 includes a waveguide 419 with a tapered portion. As the lightrays pass through the waveguide 419, the light rays are graduallytransferred through the tapered portion formed on the second core layer412 from the first core layer 410. The light rays exit the taperedportion of the waveguide 419. Positioning the second core layer 412below the first core layer 410 allows an etching on a slider for placingthe laser diode 414 to be reduced. This occurs because the first corelayer 410 is located further from the slider in the X-direction than inan implementation where the first core layer 410 is positioned below thesecond core layer 412.

FIGS. 5A-5F illustrate an example series of mode profiles representinglight passing through a waveguide at various distances from a laserdiode. Each mode profile depicts an intensity level of the light varyingwith size of the mode profile in an X-direction and a Y-direction(referencing FIG. 2).

An example waveguide is described below that generates the mode profilesdepicted in FIGS. 5A-5F. A 120 nm thick Ta₂O₅ second core layer is usedwith an index of refraction (n) equaling to 2.15. Further, an 800 nmthick SiON first core layer is used with an index of refraction (n)equaling to 1.70. The cladding layers are Al₂O₃ and have an index ofrefraction (n) equaling to 1.65. A tapered portion of the waveguide islinear, 100 μm long, with a waveguide entrance width equaling 100 nm anda tapered portion exit width equaling 600 nm. The laser diode isedge-emitting with an edge junction parallel to a waveguide plane (YZplane of FIG. 2) and centered at the first core layer. Light emittedfrom the laser diode had full divergence angles atfull-width-at-half-maximum of 7.74° parallel to the edge junction and26° normal to the edge junction.

FIG. 5A illustrates the mode profile at 1 μm from the waveguide entrancein the Z-direction. The corresponding full-width-at-half-maximumintensity (FWHM) is 0.868 μm along the X-direction and 2.270 μm alongthe Y-direction (referencing the system 200 of FIG. 2). After a 21 μmpropagation of the light through the waveguide (shown in FIG. 5B), theillustrated mode profile shrinks rapidly and a center of the lightshifts from the first core layer to the second core layer (not shown).FIG. 5C illustrates the mode profile after the light propagates 41 μmthrough the waveguide. At 41 μm, the light is almost completelytransferred to the second core layer (not shown) and illustrated modeprofile reaches a minimum Y-direction dimension (˜305 nm). With thelight propagating further in the Z-direction (see FIGS. 5D-5F), the modeprofile expands along the Y-direction slightly with an increase in widthof the waveguide taper. In this implementation, light deliveryefficiency is estimated at 87%.

The light delivery efficiency depends in part on the thickness in theX-direction (referencing FIG. 2) of the first core layer. The idealthickness for the first core layer to achieve maximum light deliveryefficiency is where the mode profile of the first core layer closelymatches the mode profile of the light coming from the laser diode. Inthe implementation shown in FIGS. 5A-5F, the ideal first core layerthickness is approximately 700 nm. However, this thickness will vary formaterials with a different refractive index.

FIGS. 6A-6B illustrate example positioning tolerances of a laser diodewith respect to the waveguide of FIGS. 5A-5F. The presently disclosedtechnology allows for a good tolerance in positioning the laser dioderelative to the waveguide. Referring to FIG. 6A, assuming that a lightdelivery efficiency (or coupling efficiency) drop from 90% to 75% isacceptable; the positioning tolerance in the X-direction isapproximately 550 nm. Referring to FIG. 6B, still assuming that a lightdelivery efficiency drop from 90% to 75% is acceptable; the positioningtolerance in the Y-direction is approximately 1,200 nm.

Emission wavelength of an edge emitting laser diode with a Fabry-Perotresonator typically varies with temperature at 0.1 nm-0.2 nm per degreeCelsius. Based on the expected temperature fluctuations (i.e. less than100° C.), the emission wavelength variation is within 20 nm. Modelingshows that the coupling efficiency variation is lower than 5% if thewavelength variation is within approximately 30 nm.

FIG. 7A illustrates light passing through the waveguide and reflectingoff of an example collimating mirror. In a YZ cross section of thecollimating mirror of FIG. 2, light passing through the waveguide iscollimated and bent 90°. A maximum ray angle from Z-axis is θ_(m) and abeam size after collimation is D. The collimating mirror is parabolic inthe YZ plane and is located z₀ away from a tapered portion exit.Assuming the coordinate (z, y)=(0, 0) is defined as the tapered portionexit, the parabolic shape of the collimating mirror may be defined as

${y = \frac{z_{0}^{2} - z^{2}}{2z_{0}}};$

wherein

z₀ is a location of the collimating mirror on the z-axis when y=0. Thebeam size (D) may then be calculated based on known θ_(m) and z₀ valuesaccording to:

${D = {{z_{2} - z_{1}} = {{{\frac{z_{0}}{\cos \; \theta_{m}}\left( {1 + {\sin \; \theta_{m}}} \right)} - {\frac{z_{0}}{\cos \; \theta_{m}}\left( {1 - {\sin \; \theta_{m}}} \right)}} = {2z_{0}\tan \; \theta_{m}}}}};$

wherein

z₁ is a first limit of the collimated beam in the z-direction,z₂ is a second limit of the collimated beam in the z-direction, andθ_(n), is a divergence angle of the light passing through the waveguidefrom the z-axis at 1/e² intensity point.

FIG. 7B illustrates collimated light reflecting off of an examplefocusing mirror and converging at a focusing point. The focusing mirrorhas two parabolic sidewalls with opening width (W) and height (H). In aYZ cross section of the focusing mirror of FIG. 2, collimated light isreflected off of the sidewalls and focused at a specific point in space(e.g., a diffraction-limited optical spot). In the implementation ofFIG. 7B, this focusing point is defined as (z, y)=(0, 0). The shape ofthe mirror may be calculated by solving for y as a function of zaccording to the following equation.

y=βz ²−1/(4β)

Further, the parameter (β) may be calculated using the followingequation,

$\beta = \frac{\frac{2H}{W} + \sqrt{1 + \left( \frac{2H}{W} \right)^{2}}}{W}$

In FIG. 7B, the focusing mirror has two complementary sidewalls. If thephase wavefront of the incident beam on the focusing mirror is uniform,the electric field of the focal point will be along the Z-direction fora TE₀ mode and X-direction for a TM₀ mode. However, some near-fieldtransducers require excitation by a longitudinally polarized focusedspot, i.e., the electric field at the focal point is along theY-direction. One way to achieve a longitudinally focused spot is to usetwo sidewalls with differing shapes. Assuming β_(L) is a shape parameterfor the left sidewall, β_(R) of a shape parameter for the right sidewallcan be calculated by

${\beta_{R} = \frac{1}{\frac{1}{\beta_{L}} + \frac{\lambda}{n_{eff}}}};$

wherein

λ is a wavelength of light rays in free space, andn_(eff) is an effective mode index of the waveguide where the focusingmirror is located.

Referring back to FIG. 2, in some implementations the transducer headslider 202 is especially narrow in the Z-direction and/or the laserdiode 214 is especially long in the Z-direction. In theseimplementations, the orientation of the collimating mirror 218 andfocusing minor 220 of FIG. 2 does not yield a focusing point 224 (ordiffraction-limited optical spot) near a center of the slider 202 in theZ-direction where the write pole 226 is located. FIGS. 8A-9B illustratemirror and mirror orientations that move the focusing point 224 in thenegative Z-direction to align the focusing point 224 with the write pole226, in the Z-direction.

FIG. 8A illustrates an example laser-in-slider light delivery system800, where a collimating mirror 818 is oriented so that light rays 834reflecting from the collimating mirror 818 propagate toward an angled,double-sided, focusing mirror 820. The system 800 of FIG. 8A includes alaser diode 814, a waveguide 816, the collimating mirror 818, and thefocusing mirror 820 as described with respect to FIG. 2. However, ashape and/or orientation of the collimating mirror 818 and the focusingmirror 820 are changed so that a focusing point 824 moves in a negativeZ-direction (referencing FIG. 2).

More specifically, light rays 834 passing through the waveguide 816 arecollimated and reflected off of the collimating mirror 818. Thecollimating mirror 818 reflects the light rays 834 in a negativeZ-direction as well as a negative Y-direction. In order to capture theangled collimated light rays 834, the focusing mirror 820 is similarlyangled and directs focused light rays 834 to a focusing point 824shifted in the negative Z-direction when compared to the focusing point224 of FIG. 2.

FIG. 8B illustrates an example laser-in-slider light delivery system 800where a collimating mirror 821 is oriented so that light rays 834reflecting from the collimating mirror 821 propagate toward an angled,single-sided, focusing mirror 823. While the implementation of FIG. 8Bis similar to the implementation of FIG. 8A, the focusing mirror 823 issingle-sided instead of double-sided. A single-sided focusing mirror haspotential advantages of being less complex to design and/or manufactureand it occupies less space than an equivalent double-sided focusingmirror. However, the single-sided focusing mirror is likely to produce alarger, less-confined focusing point 824 than the double-sided focusingmirror.

FIG. 9A illustrates an example laser-in-slider light delivery system 900where two straight mirrors 936 are used to shift light rays 934reflecting from the collimating mirror 918. The system 900 of FIG. 9Aincludes a laser diode 914, a waveguide 916, the collimating mirror 918,and the focusing mirror 920 as described with respect to FIG. 2.However, two additional straight mirrors 936 are incorporated to shiftthe focusing point 924 in a negative Z-direction (referencing FIG. 2).

More specifically, light rays 934 passing through the waveguide 916 arecollimated and reflected off of the collimating mirror 918. However, inthe implementation of FIG. 9A, the collimated light rays 934 do notproceed directly to the focusing mirror 920. Instead, the collimatedlight rays 934 are first reflected off a straight mirror 936 in thenegative Z-direction and then off another straight mirror 936 in thenegative Y-direction. The collimated light rays 934 then are directed toa focusing point 924 by the focusing mirror 920 as described with regardto FIG. 2. The net effect of the two straight mirrors 936 is that thefocusing point 924 is shifted in the negative Z-direction when comparedto the implementation of FIG. 2.

FIG. 9B illustrates an example laser-in-slider light delivery system 905where a straight mirror 936 and a split straight mirror are used toshift light rays 934 reflecting from the collimating mirror 918. Whilesimilar to the implementation of FIG. 9A, FIG. 9B illustrates a splitstraight mirror 938 with one half of the split straight mirror 938shifted transversely in the Z-direction (Δz). The additional straightmirrors 936 and/or split straight mirror 938 in the implementations ofFIGS. 9A and 9B decrease a light delivery efficiency of the system 905due to Fresnel reflection loss.

The split straight mirror 938 is utilized in order to reduce oreliminate light rays 934 directed to a bottom of the focusing mirror920, where the light rays 934 are not effectively reflected to thefocusing point 924. This is referred to herein as reducing oreliminating obscuration in the focusing mirror 920. Further, the splitstraight mirror 938 may be utilized to introduce a phase shift in thelight rays 934 directed to the focusing mirror.

In one implementation, the amount of shift (Δz) of the split straightmirror 938 can be calculated according to

${\Delta \; z} = {{m\frac{\lambda}{n_{eff}}} \leq \frac{1}{\beta}}$

where m is a positive integer representing 1, 2, 3 . . . , whichsatisfies above inequality, λ is a wavelength of the-light rays 934 infree space, n_(eff) is an effective mode index of the waveguide 916where the focusing mirror 920 is located, and β is a parameterdescribing the shape of the focusing mirror 920.

The split straight mirror 938 may also be utilized to achieve alongitudinally focused spot as discussed with regard to FIG. 7B.Further, the collimating minor 918 and/or focusing mirror 920 may alsobe split to achieve a longitudinally focused spot. In the implementationof FIG. 9B, the distance (Δz) to achieve a π phase-shifted wavefront isgiven by

${\Delta \; z} = {{\left( {m + \frac{1}{2}} \right)\frac{\lambda}{n_{eff}}} \leq {\frac{1}{\beta}.}}$

In implementations where the collimated beam after the collimator 918 isparticularly small and the distance from the collimator 918 to thefocusing mirror 920 is much longer than the Rayleigh distance,

$\frac{{\pi \left( {0.5D} \right)}^{2}}{\lambda},$

the collimated beam from the collimator 918 may become divergent as thelight propagates toward the focusing mirror 920. This is due todiffraction of the light beam. To compensate for imperfect collimation,the final beam size incident on the focusing mirror 920 can be adjustedand the phase wavefront can be corrected by replacing the straightmirror 936 with a concave mirror.

FIG. 10 is a flow chart illustrating example operations 1000 fordirecting light from a light source, through a waveguide, and focusingthe light on a magnetic media for heat assisted magnetic recording.Light from a light source is received into a first core layer of awaveguide on a recording head in operation 1005. The light has a firstmode profile associated with the light source (e.g., native to the lightsource). The light is gently transferred to a second layer of thewaveguide over a length of the waveguide in operation 1010. When thelight is transferred to the second layer, the mode profile is graduallychanged to a second mode profile.

The light with the second mode profile is then output to a collimatingminor in operation 1015. The collimating minor then collimates divergentlight rays passing through the waveguide and re-directs the collimatedlight to a focusing mirror in operation 1020. The focusing mirrorfocuses the light on a spot on the magnetic recording media in closeproximity to a spot of the magnetic recording media where data will bewritten in operation 1025. In alternate implementations, the focusingminor focuses the light on a near-field transducer rather than a spot onthe magnetic recording media. The near-field transducer then furthercondenses the light to the spot on the magnetic recording media.

While implementations of the waveguide, collimating mirror, and/orfocusing minor disclosed herein are discussed specifically with regardto heat assisted magnetic recording technology applications, thepresently disclosed technology is equally applicable to any opticssystem (e.g., photonic integrated circuits) where precise light deliveryat very low loss is desired. For example, the presently disclosedtechnology may be applied to fibre-optic communication systems,biomedical devices, and photonic computing devices, for example.

The above specification and examples provide a complete description ofthe structures of exemplary implementations of methods and apparatusthat may be used for light delivery for heat assisted magneticrecording. Although various implementations of the method and apparatushave been described above with a certain degree of particularity, orwith reference to one or more individual implementations, those skilledin the art could make numerous alterations to the disclosedimplementations without departing from the spirit or scope of thepresently disclosed technology. It is intended that all matter containedin the above description and shown in the accompanying drawings shall beinterpreted as illustrative only of particular implementations and notlimiting. The implementations described above and other implementationsare within the scope of the following claims.

1. A waveguide comprising: a first core layer configured to receivelight from a light source and transmit the light at a first mode profileassociated with the light source; and a tapered portion of a second corelayer configured to receive the light from the first core layer andtransform the light to a second more confined mode profile.
 2. Thewaveguide of claim 1, further comprising: a collimating mirror having amode profile that matches the second mode profile.
 3. The waveguide ofclaim 1, wherein the first core layer includes a material having a firstrefractive index and the second core layer includes a material having asecond refractive index that is greater than the first refractive index.4. The waveguide of claim 1, wherein the light transfers from the firstcore layer to the second core layer along a length of the taperedportion of the second core layer of the waveguide.
 5. The waveguide ofclaim 1, further comprising: one or more cladding layers adapted toconfine the light within the first core layer and the second core layer.6. The waveguide of claim 1, wherein the first core layer includes twoor more sublayers.
 7. The waveguide of claim 1 incorporated in a heatassisted magnetic recording head.
 8. The waveguide of claim 1 mounted ona recording head slider.
 9. The waveguide of claim 1 mounted on atrailing edge of a recording head slider.
 10. A method of directinglight from a light source, the method comprising: receiving light into afirst core layer of a waveguide at a first mode profile; transferringthe light from the first core layer to a tapered portion of a secondcore layer of the waveguide; and outputting the light from the taperedportion of the second core layer of the waveguide at a second moreconfined mode profile.
 11. The method of claim 10, further comprising:focusing the light onto a magnetic media to heat a spot on the magneticmedia.
 12. The method of claim 11, wherein the focusing operation isaccomplished using one or both of a focusing mirror and a near-fieldtransducer.
 13. The method of claim 10, further comprising: reflecting acollimated beam of light having a desired width from a collimatingmirror using the light output from the tapered portion of the waveguide;14. The method of claim 10, wherein the light transfers from the firstcore layer to the second core layer along a length of the taperedportion of the waveguide.
 15. A method of directing light from a lightsource, the method comprising: receiving light into a waveguide at afirst mode profile associated with the light source; outputting thelight at a second mode profile that is more confined than the first modeprofile; and reflecting a collimated beam of light having a desiredwidth from a collimating mirror using the light output.
 16. The methodof claim 15, further comprising: focusing the collimated beam of lightonto a magnetic media to heat a spot on the magnetic media.
 17. Themethod of claim 16, wherein the focusing operation is accomplished usingone or both of a focusing mirror and a near-field transducer.
 18. Themethod of claim 15, wherein a shape of the collimating mirror may bewritten in terms of y as a function of z using${y = \frac{z_{0}^{2} - z^{2}}{2z_{0}}},$ and wherein z₀ is a locationof the collimating mirror on the z-axis when y equals
 0. 19. The methodof claim 15, wherein the desired width D of the collimated beam may becalculated using${D = {{z_{2} - z_{1}} = {{{\frac{z_{0}}{\cos \; \theta_{m}}\left( {1 + {\sin \; \theta_{m}}} \right)} - {\frac{z_{0}}{\cos \; \theta_{m}}\left( {1 - {\sin \; \theta_{m}}} \right)}} = {2z_{0}\tan \; \theta_{m}}}}},$and wherein z₀ is a location of the collimating mirror on the z-axiswhen y=0, z₁ is a first limit of the collimated beam in the z-direction,z₂ is a second limit of the collimated beam in the z-direction, andθ_(m) is ½ a divergence angle of the light passing through thewaveguide.
 20. The method of claim 15, further comprising: reflectingthe collimated beam of light from two or more straight mirrors tolaterally shift the collimated beam of light.